The corrugating devices of prior art machines of this type consist of corrugating rollers in the form of rotatable shafts on which rings are mounted or formed having a cross-sectional shape corresponding to the desired profile to be imparted to the sheet at the station comprising the two corrugating devices at issue. More particularly, the rings of the first or front working station are fairly thin to give shallow corrugations in a first working pass, whereupon the radial thickness of the corrugations is increased successively at subsequent stations in order to give, at a last station, the desired final corrugation depth. In actual practice, however, the use of such ring-carrying shafts as corrugating devices suffers from a number of shortcomings. Since the rings are fixedly mounted on their associated shafts, the peripheral speed at the circumferential or ridge surface of the ring will be different from the peripheral speed of the neighbouring furrows forming portions of the shaft proper, which have a smaller diameter than the ring. This means that the sheet which is being worked will constantly partially slip when in contact with the respective surfaces, and this may lead to inadequate precision and surface damage in the finished product. Furthermore, readjustment of the various corrugating devices of the machine from one corrugation type to another is extremely complicated and time-consuming. For example, readjustment of a prior art machine comprising about 20 working stations may take from 25 to 35 days' work, and this means that small and medium-sized manufacturers are subjected to extensive and costly interruptions when shifting from one corrugation type to another. To large-scale manufacturers with many corrugation types on their production program, such long interruptions are unacceptable, and they are therefore compelled to acquire a separate corrugating machine for each individual corrugation type on their program. This in turn implies extremely high capital costs, and even then long interruptions cannot be avoided if the machine cannot be operated to capacity over a longer period of time.